This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-179214, filed Jun. 25, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to an active matrix substrate for a liquid crystal display device and a method of manufacturing the same.
Liquid crystal display devices (LCD) are advantageous since they are formed thin and display color images with low power consumption. By virtue of these advantages, the LCDs are widely used for lap-top personal computers. The image quality of the LCDs is good enough to be employed not only for electric-data display devices but also for TV screens.
Of the LCD devices, an active matrix type LCD is used as a flat panel display capable of providing full-color images with a high quality. The active matrix type LCD is formed of a first glass substrate, a second glass substrate and liquid crystal which is injected between the first and the second glass substrate. In the first glass substrate, thin transistors (TFT), which employ amorphous silicon or poly crystalline silicon as an active layer, are arranged in a matrix form. The second glass substrate is fixed so as to face the first glass substrate with a gap of about 5 xcexcm interposed between them.
FIG. 1 shows a cross-sectional view of a pixel portion of a conventional active matrix type LCD. A scanning line 3502 and a storage capacitor line 3503 are formed on a glass substrate 3501. A gate insulating film 3504 is formed over the lines 3502 and 3503. Furthermore, a pixel electrode 3505 is selectively formed on the gate insulating film 3504.
Reference numeral 3506 is a TFT portion, which is formed of a semiconductor layer 3507, a channel protecting insulating film 3508 formed on the semiconductor layer 3507, and two doped semiconductor layers 3509 facing each other. The two doped semiconductor layers are formed in contact with the semiconductor layer 3507 while an end portion of each of the doped semiconductor layers is mounted on the channel protecting insulating film 3508. A source electrode 3510 and a drain electrode 3511 are formed respectively on the two doped semiconductor layers 3509. The source electrode 3510 is connected to a signal line (not shown). The drain electrode 3511 is connected to the pixel electrode 3505. A protective insulating film 3512 is formed over the TFT portion 3506.
With recent technical development, a field of view has been widened. Accordingly, a narrow viewing angle of the LCD has been overcome. In addition to this, since the TFT array can be formed on the glass substrate, a relatively large display having a diagonal length of about 10 to 25 inches has been realized.
However, to realize a high definition TV (HDTV), a large screen having a diagonal length of about 40-60 inches is desired. To manufacture the TFT array for such a large screen, it is necessary to construct an assembly line capable of holding an ultra-large glass substrate larger than 1 m square. A large equipment cost is inevitably required.
A method of making the large screen by jointing a plurality of substrates carrying TFT arrays is disclosed in Japanese Patent Applicaltion KOKAI publication No. 10-268332. However, this method has the following problems. Since the substrates are not jointed accurately, an aperture ratio of the joint portion is low. It is difficult to accurately control the level of the joint portion between the substrates, taking the thickness (5 xcexcm) of the liquid crystal layer into consideration. Therefore, a large quantity of the substrates are not manufactured.
On the other hand, a mobile data terminal equipment providing electronic data anytime and anywhere was developed by making use of xe2x80x9clow power consumptionxe2x80x9d of the LCD. The mobile data terminal equipment has been used in a wide variety of fields. In future, it is expected that electronic data will be displayed with the same ultra precision as that of printing matter, that is, about 150-300 pixel/inch (ppi).
These mobile data terminal equipments have to be formed light with a low power consumption. When a liquid crystal display is formed on an A4-size glass substrate of about 0.7 mm-thick, the total weight of the display results in 220 g. If the weight of the bezel for fixing the display is included, the total weight of the device will be about 400 g or more.
The weight of the display device can be reduced by about xc2xd if a plastic substrate is employed. The weight can be further reduced, if a film substrate is used. Such a display device is suitable for use in the mobile data terminal equipment. In these circumstances, attempts have been made to form the TFTs on the plastic substrate or the film substrate. When the TFTs are formed on these substrates, however, it is necessary to reduce the processing temperature. If the TFTs are formed at a low processing temperature, performance of the TFTs may be degraded, with the result that limitations may be imposed on image quality and the number of pixels. Furthermore, the thermal expansion coefficiency of these substrates is high and plastic deformation occurs at a low temperature. For these reasons, it is conceivable that the high definition display device may not be attained.
An object of the present invention is to provide an active matrix substrate for achieving the formation of a high definition image at a low cost even if a large substrate or a non-glass substrate is used, and also provide a method for manufacturing the same.
According to a first aspect of the present invention, to attain the aforementioned objects, there is provided a method of manufacturing an active matrix substrate comprising:
a first step of forming a plurality of elements on a first substrate;
a second step of forming wirings on a second substrate;
a third step of transferring some elements selected from the plurality of elements onto the second substrate from the first substrate; and
a fourth step of selectively connecting the some elements transferred onto the second substrate to the wirings.
According to a second aspect of the present invention, there is provided a method of manufacturing an active matrix substrate comprising:
a first step of forming a plurality of elements on a first substrate;
a second step of transferring some elements selected from the plurality of elements onto a second substrate from the first substrate;
a third step of forming wirings on the second substrate after the second step; and
a fourth step of selectively connecting the some elements and the wirings.
In the methods of manufacturing an active matrix substrate according to the first and second aspects, it is preferable that the following steps be carried out.
The third step includes the steps of:
adhering the plurality of elements formed on the first substrate onto the third substrate;
etching away the first substrate; and
transferring the some elements selected from the plurality of elements adhered on the third substrate to the second substrate.
The third step includes the steps of:
forming an adhesion layer on the third substrate;
transferring the plurality of elements formed on the first substrate onto the third substrate via the adhesion layer; and
selectively heating portions of the adhesion layer on which the some elements are formed, to thereby transfer the some elements from the third substrate to the second substrate.
In the aforementioned step, the elements may be removed from the element formation substrate by laser irradiation in place of heat application. Alternatively, the elements formed on the element formation substrate may be transferred on the adhesion layer which is heated and further transferred from the intermediate transfer substrate to the final substrate by UV irradiation.
The third step includes a step of selecting the some elements such that a largest interval of two adjacent elements arbitrarily chosen from the some elements is larger than a largest interval of two adjacent elements arbitrarily chosen from the plurality of elements formed on the first substrate.
The third step includes a step of selecting the some elements at predetermined intervals thereamong, and a step of repeating the step of selecting the some elements.
The first step includes the steps of:
forming an underlying layer on the first substrate;
forming the plurality of elements on the underlying layer; and
forming a protective layer individually on each of the plurality of elements, such that the plurality of elements are covered with the underlying layer and the protective layer.
The method of the present invention further comprises a step of separating the underlying layer into sections such that the underlying layer remains only just under each of the plurality of elements.
Note that the underlying layer is desirably a stacked layered composed of an etching stopper layer formed on the first substrate and an undercoat layer formed on the etching stopper layer.
According to a third aspect of the present invention, there is provided a method of manufacturing an active matrix substrate comprising:
a first step of forming an underlying layer on a first substrate;
a second step of forming a plurality of circuit units, on the underlying layer, composed of at least one element and at least one wiring connected to the at least one element;
a third step of adhering the plurality of circuit units formed on the first substrate to a third substrate via an adhesion layer formed on the third substrate;
a fourth step of etching away the first substrate; and
a fifth step of selectively transferring the plurality of circuit units adhered onto the third substrate to the second substrate.
The method of manufacturing an active matrix substrate according to the third aspect of the present invention may be carried out as follows.
The fifth step includes a step of selectively heating portions of the adhesion layer on which some circuit units to be transferred are formed, to thereby transfer the circuit units from the third substrate to the second substrate.
The second step includes a step of forming a protective layer individually on each of the plurality of circuit units, such that the plurality of circuit units are covered with the underlying layer and the protective layer.
The method according to a third aspect of the present invention further comprises a step of separating the underlying layer into sections such that the underlying layer remains only just under each of the plurality of circuit units.
The first step includes a step of forming a stacked-layer film composed of an etching stopper layer on the first substrate and an undercoat layer formed on the etching stopper layer.
Each of the plurality of circuit units includes a plurality of pixel electrodes, and the fifth step is repeated a plurality of times such that an interval between adjacent electrodes of the plurality of pixel electrodes is kept substantially constant through the plurality of circuit units transferred.
According to a fourth aspect of the present invention, there is provided an active matrix substrate comprising:
a substrate;
an adhesion layer formed on the substrate;
an undercoat layer formed on the adhesion layer
a plurality of elements formed on the undercoat layer;
wherein the adhesion layer and the undercoat layer are separated such that the adhesion layer and the undercoat layer remain only just under each of the plurality of elements.
A substrate formation substrate for use in manufacturing the active matrix substrate comprises:
a substrate;
an exfoliation layer formed on the substrate for being removed by heat application; and
elements formed on the exfoliation layer at the same height, the elements being electrically isolated from each other.
An intermediate transfer substrate for use in manufacturing the active matrix substrate comprises:
a substrate;
an exfoliation layer formed on the substrate for being removed by heat application;
elements formed on the exfoliation layer at the same height, the elements being electrically isolated from each other.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.